An actuator which is integrated in a scanning device is used for emission of a light beam (laser beam) onto an optical disk in the form of an information storage medium, and for reception of the beam reflected from it. For this purpose, the actuator has a focus lens and is attached, such that it can be adjusted, by means of a mount to an optical housing, which is also known as pick-up and can be moved on guide rails, in order to allow the focus lens to be aligned with the optical path of the housing. This housing and thus the entire scanning device can be moved at high speed and with high positioning accuracy, driven by one or more electric motors, and ensures short access times to different points on the recording medium. In this case, the scanning device focuses a radiation beam, in order to form a radiation point, on a track that is to be scanned on the disk. This radiation point follows the track on the rotating disk during recording or reproduction. This is done with the aid of a track control system, which allows coarse control of the slide-like housing and of the actuator in a radial direction with respect to the disk, and allows fine control of the actuator. This fine control is required in order to keep the distance between the focus lens and the optical disk constant, and in order to ensure precise tracking of the projected light beam, since the disk normally has an unavoidable eccentricity error, which leads to inadvertent oscillations during operation which would themselves lead to reproduction errors, without fine control.
The actuator is preferably attached to the optical housing by means of a mounting board and has a lens holder for the focus lens, a damper base, which is fixed to the mounting board, for the lens holder, and focus coils which interact with a magnet arrangement, tracking coils and, possibly, also tilt coils, with the lens holder being connected in an elastically sprung manner to the damper base via elastically flexible suspension means, in particular also wires. In order to reduce the mass of the actuator, so that its moment of inertia is less and it can be controlled more sensitively and quickly, the coils may be arranged as printed coils on a printed circuit board (coil printed circuit board), which is connected to the lens holder.
An actuator with a plastic lens holder is described in JP-A-2003-346361. In this case, the magnet arrangement is arranged on only one side of a coil printed circuit board, on which focus and tracking coils are printed, and is thus positioned such that the coils are in the magnetic field. This coil printed circuit board, the lens holder and a so-called substrate holder composed of metal for the coil printed circuit board are positioned next to one another and are connected to one another by means of a large number of projections, which are arranged on the substrate holder, and form the moving parts of the actuator. This means that the substrate holder composed of metal is also moved as a component of the moving part.
US-A-2002/0075575 also discloses, in the description of the prior art, an actuator having a coil printed circuit board. In this case, the coil printed circuit board is arranged between two magnets, and the focus lens is positioned with a part of a lens holder, which is connected to the coil printed circuit board, in the area between the damper base and the coil and magnet arrangement. The other part of the lens holder surrounds the coil and magnet arrangement on the side facing away from the focus lens, and, together with the focus lens, forms the moving part of the actuator. The lens holder thus has a considerable mass and a correspondingly high moment of inertia.